1. Field of the Invention
The present invention relates to a process for production of a styrene or styrene derivative polymer of narrow molecular weight distribution.
2. Description of the Prior Art
Various polymers are currently in production by polymerization of a vinyl compound using a radical polymerization initiator. Polymerization of a vinyl compound is also possible by using other polymerization initiator, i.e. an ionic polymerization initiator composed of a metal compound, whereby can be produced a polymer having a molecular weight distribution of smaller than 2 [the molecular weight distribution is generally expressed by the ratio (Mw/Mn) of weight-average molecular weight (Mw) and number-average molecular weight (Mn)].
In the above ionic polymerization, however, since a highly reactive polymerization initiator is used, presence of impurities (e.g. small amount of water and active-hydrogen-containing compound) in the reaction system hinders the polymerization reaction and allows the produced polymer to have a broad molecular weight distribution.
It was reported in Macromolecules, 26, 2987-2988 (1993) that polymerization of styrene using 2,2,6,6-tetramethyl-1-piperidinyloxy free radical (hereinafter abbreviated to TEMPO) (this is a nitroso radical compound) and benzoyl peroxide (an ordinary radical polymerization initiator) provided a styrene polymer of very narrow molecular weight distribution. This polymerization process, unlike the hereto for known process for production of styrene polymer of narrow molecular weight distribution wherein styrene polymerization is conducted at a low temperature using sodium naphthalene as the polymerization initiator, uses an ordinary radical polymerization initiator and accordingly makes simple the polymerization procedure; however, the polymerization rate is very low and a time as long as 69 hours is required to attain a conversion of, for example, 90% (number-average molecular weight of produced styrene polymer=7,800, molecular weight distribution thereof=1.27).
Also, in U.S. Pat. No. 5,322,912 is disclosed a process wherein a protonic acid (e.g. a sulfonic acid or a carboxylic acid) is added to a free radical polymerization system in order to achieve a high polymerization rate. The polymer obtained by this process, however, contains the protonic acid used and accordingly has limited applications.